Space used by nulls in database

Question

If a column is null, does that affect the space used by the column? Is the space used fixed by the column definition? Does this vary from database to database. (I am mainly

Answer 1

It's stored in a bitmap, not as a column value.

Example: a nullable varchar column called middle name

• row 1, "bob" is stored as an offset, 3 bytes for bob, 2 bytes for length of "bob"
• row 2, NULL row is not stored as a value like "bob", but in the row header

Unless you have a very small table, say a single column char(1), then it's more efficient

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